After their bullpen's worst performance of the season, the Boston Red Sox are hoping a converted reliever can help them bounce back.

With Alfredo Aceves making his first start in nearly two years, the Red Sox will try to win the series finale against the Baltimore Orioles on Thursday night.

Boston's bullpen had a respectable 3.92 ERA during the team's 5-2 start before closer Joel Hanrahan allowed five runs in the ninth inning of Wednesday's 8-5 defeat at Fenway Park. Manny Machado hit a tiebreaking three-run homer and Chris Davis had a solo shot to give Hanrahan his first blown save in four chances for the Red Sox (5-3).

"It was a huge win for us," Machado said after his first homer of the year. "To come out with the victory is just going to give us the big boost that we needed to get this show rolling."

The Red Sox bullpen was without Aceves, who is set to replace the injured John Lackey in the rotation. Lackey went on the disabled list Monday with a strained right biceps, and left-hander Felix Doubront's start is being pushed to Friday.

"We wanted another right-hander in this ballpark against Baltimore," manager John Farrell told the team's website. "Alfredo has had some good performance numbers against some individuals in their lineup."

Aceves is 2-1 with a 4.18 ERA in nine all-time starts, the most recent June 21, 2011, and he tossed six scoreless innings in his only one against Baltimore, a win for the New York Yankees on Sept. 20, 2008.

Aceves (0-0, 10.38 ERA), though, has had trouble keeping the ball in the park in his two appearances this season. He gave up a three-run homer to the Yankees' Vernon Wells on April 3 and another three-run shot to Toronto's Colby Rasmus three days later.

"(Aceves is) certainly capable of being a good starting pitcher. He has the pitches in the mix. He's excited for the opportunity. We'll see how it goes," general manager Ben Cherington told the team's website.

The Orioles (4-4), winners in 18 of 25 over the Red Sox, are hoping Chris Tillman can continue his success against Boston. The right-hander is 1-0 with a 1.52 ERA in his last four starts against the Red Sox, and has a 0.82 ERA in his two at Fenway but the Orioles lost both starts.

Tillman (0-0, 12.27), though, heads into this start following a difficult season debut. He didn't make it past the fourth inning Saturday in a 6-5 loss to Minnesota while allowing five runs, seven hits and four walks.

"I was real pleased with the stuff he featured, just couldn't get into a consistent rhythm after that first inning," manager Buck Showalter told the team's website. "He'll be better."

Dustin Pedroia is 4 for 11 (.364) in his career against Tillman but the rest of the current Red Sox roster is a combined 6 for 30 (.200) with seven strikeouts.

Baltimore's Adam Jones is 6 for 18 (.333) with three extra-base hits against Aceves, but J.J. Hardy (3 for 18), Davis (2 for 12), Matt Wieters (1 for 12) and Nolan Reimold (1 for 10) haven't fared as well.